Musnad Ahmad 132:13

Hassan narrated to us, Ibn Lahi'ah narrated to us, from Zabban, from Sahl ibn Mu'adh, from his father, from the Messenger of Allah (peace and blessings of Allah be upon him), that he used to say: "The one who laughs in prayer, the one who turns [his head], and the one who cracks his fingers are all in the same position."